CN102646169B - Method for calculating mean free path (MFP) of exploration rover against complex terrain environment - Google Patents

Abstract

The invention discloses a method for calculating a mean free path (MFP) of an exploration rover against complex terrain environment, which comprises selecting a locating point and a running direction of the exploration rover; judging passibility of a projection region of the exploration rover body; and calculating the MFP. The invention really reflects the exploration environment of the exploration rover by establishing a digital elevation map (DEM) of star terrain, and can be applied to complex terrain environment having various obstacles (such as slopes and irregular obstacles), and the calculation accuracy is not affected by the complex degree of terrain. The invention calculates the MFP by rotating the DEM of the star terrain at a fixed angle interval and straightly moving along the fixed direction on each map, simplifies the algorithm complicacy, and simultaneously improves the simulation rate. The method adopts the slope and elevation difference as a termination judgment condition of a single MFP calculation, and comprehensively considers climbing capacity and obstacle clearance capacity of the exploration rover.

Description

A kind of inspection prober mean free path computing method for complex-terrain

Technical field

The invention belongs to aerospace field, relate to the computing method of inspection prober mean free path, specially refer to a kind of inspection prober mean free path computing method that are directed to complex-terrain.

Background technology

Outside the moon, Mars etc., celestial body input inspection prober is the key link in survey of deep space field.Mean free path (Mean Free Path, MFP) be a relevant statistical measures of ability of encountering the probability of barrier with inspection prober and breaking the barriers, it is defined as: in specific landform, before must changing travel direction, the mean path of inspection prober institute energy straight line moving.Its main application has following two aspects: (1), under specific landform, evaluates the travelling performance of inspection prober, for inspection prober size Selection, suspension design, chassis design provide foundation.(2), in the situation that inspection prober is definite, evaluate the quality of landform passability, for the selection of touchdown area and the evaluation of touchdown area safety coefficient provide foundation.At present, the computing formula of mean free path is proposed in < < Rover Chassis Evaluation and Design Optimizations Using the RCET > > by people such as S.Michaud, first for the barrier that hinders inspection prober roaming in certain area, with diameter, its size is described; Then add up the number of different-diameter scope barrier in this region, based on following formula, realize the calculating of mean free path:

$x=\frac{1-\frac{b}{2}\underset{i=i_0}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{D}_i{N}_i-\frac{1}{2}\underset{i=i_0}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{D}_i^2{N}_i}{b\underset{i=i_0}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{N}_i+\underset{i=i_0}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{D}_i{N}_i}---\left(1\right)$

In formula: b is width of the carbody, D is for hindering the barrier diameter of inspection prober roaming, and N is that every square metre of scope interior diameter is the number of the barrier of D～D+ δ D; Subscript i represents different barriers.

In actual applications, due to celestial body surface environment more complicated, there is following defect in existing mean free path computing formula: has only considered only to exist in subdued topography the situation of similar round barrier, if the barrier of the obstruction inspection prober roamings such as the rock coming in every shape, hole moat is all reduced to the circular barrier of certain diameter, process, inevitably bring certain error; When there is the landform such as slope, mean free path computing formula has only been considered the obstacle climbing ability of inspection prober, and has ignored the checking to its climbing capacity, and the method for calculating mean free path by formula can not be considered other travelling performances outside obstacle climbing ability.

Summary of the invention

The problems referred to above that exist for solving prior art, the present invention proposes a kind of inspection prober mean free path computing method for complex-terrain environment, its computational accuracy is not subject to the impact of Topographic Complex Degree, can be applicable to exist in the terrain environment of all kinds barrier; In mean free path computation process, not only to consider the obstacle climbing ability of inspection prober, also will consider the climbing capacity of inspection prober, and can add arbitrarily other travelling performance indexs; Reduce algorithm complex, effectively improve computing velocity.

Technical scheme of the present invention is: a kind of inspection prober mean free path computing method that are directed to complex-terrain environment, comprise the following steps:

The selection of A, inspection prober anchor point and travel direction

A1, generation celestial body landform digital elevation figure Digital Elevation Map, DEM

The terrain data of certain celestial body surf zone of being described by digital elevation model is one group of tri-vector finite sequence, is: V with the formal description of function _i=(X _i, Y _i, Z _i) (i=1,2,3 ..., n), wherein, X _i, Y _iplanimetric coordinates, Z _ix _i, Y _icorresponding elevation; In Matlab software, first programme and realize the scope extraction of planimetric coordinates and elevation, find directions X minimum value X _minwith maximal value X _max, Y-direction minimum value Y _minwith maximal value Y _max, Z direction minimum value Z _minwith maximal value Z _max; Then, determine the bulk of each pixel representative in map and the height value of different gray-scale value representatives, set up the digital elevation figure describing with gray level image, wherein, the gray-scale value of 0-255 and Z _min-Z _maxbetween be linear mapping relations;

A2, selection travel direction

The mean value that mean free path is the free path repeatedly selecting at random reference position and travel direction and obtain, need to expend very long simulation time; In order to reduce algorithm complex, improve simulation velocity, select to press fixed angle interval rotation celestial body landform digital elevation figure DEM, the method for then all travelling along fixed-direction on every width figure averages free path and calculates, the complicacy that while avoiding random choice direction to travel, car body view field is calculated;

A3, random selecting point travel

After definite fixedly travel direction, in every width celestial body landform digital elevation figure DEM, the random starting point of selecting is as the central point of inspection prober starting, extracts the central point landform altitude data in car body drop shadow spread around according to car body size in celestial body landform digital elevation figure DEM;

B, inspection prober car body view field passability are judged

Passability judgement comprises two aspects, the one, and gradient restriction, another is vertical height restriction, both are all single free path and calculate the decision condition stopping; If inspection prober is wide, be b, obstacle climbing ability is that vertical height is h, and the gradient that can ascend is restricted to θ; Wherein, step B1 is that the gradient is judged, step B2 is that vertical height is judged; When both are all inspection prober by result of determination, can pass through, judge that car body view field can pass through;

Landform altitude data in B1, selection car body drop shadow spread, utilize least square method to carry out space plane matching, the space plane parameter obtaining according to matching obtains the grade information of car body view field, according to the driveability of inspection prober, the gradient is greater than θ and is and can not passes through this region, calculates one of decision condition stopping as single free path;

B2, in the region of the anterior overall width b*h/tan θ of view field, search for minimum height value and maximum elevation value, if both differences are greater than h, think and exceed obstacle climbing ability scope, can not pass through, as single free path, calculate another decision condition stopping;

C, mean free path are calculated

During each simulation calculation free path, take keeps straight on runs into and can not repeatedly add up rear sum-average arithmetic by locating, as terminal, to obtain the longest air line distance that single can travel, and just can obtain mean free path.

Compared with prior art, beneficial effect of the present invention and benefit are:

1, the mean free path computing method that the present invention proposes, by setting up celestial body landform digital elevation figure DEM, the acquisition environment of true reflection inspection prober, can be applicable to for example exist, in the complex-terrain environment of all kinds obstacle (slope and irregular slalom), and computational accuracy is not subject to the impact of Topographic Complex Degree.

2, the present invention is by scheming by fixed angle interval rotation celestial body landform digital elevation figure DEM, and the method for all keeping straight on along fixed-direction on every width figure averages free path calculating, reduced algorithm complex, improved simulation velocity simultaneously.

3, the present invention utilizes the landform altitude data of inspection prober car body view field, carry out plane fitting and obtain view field's grade information, car body view field search for minimum height value and maximum elevation value and do poor, the gradient and elevation value difference are calculated to the decision condition stopping as single free path, considered climbing capacity and the obstacle climbing ability of inspection prober.

4, the present invention can arbitrarily increase new single free path calculating stop technology condition in step B, for example, considers that the degree of roughness of landform surpasses a certain threshold value etc.So the present invention can consider other travelling performance indexs outside obstacle climbing ability in mean free path is calculated.

Accompanying drawing explanation

The present invention has accompanying drawing 15 width, wherein:

Fig. 1 is the celestial body landform digital elevation figure DEM in certain lunar surface landform region.

Fig. 2 is 5 ° of degree celestial body landform digital elevation figure DEM rotation examples.

Fig. 3 is 10 ° of degree celestial body landform digital elevation figure DEM rotation examples.

Fig. 4 is 20 ° of degree celestial body landform digital elevation figure DEM rotation examples.

Fig. 5 is 30 ° of degree celestial body landform digital elevation figure DEM rotation examples.

Fig. 6 is 45 ° of degree celestial body landform digital elevation figure DEM rotation examples.

Fig. 7 is 90 ° of degree celestial body landform digital elevation figure DEM rotation examples.

Fig. 8 is 180 ° of degree celestial body landform digital elevation figure DEM rotation examples.

Fig. 9 is 315 ° of degree celestial body landform digital elevation figure DEM rotation examples.

Figure 10 is the car body view field extracting along working direction.

Figure 11 is that grade information is obtained in space plane matching.

Figure 12 is that in car body view field, minimum height value and maximum elevation value hunting zone are determined.

Figure 13 is the result that 315 ° of rotation celestial body landform digital elevation figure DEM proceed to 3000 free path simulation calculation.

Figure 14 is the free path statistics curve that carries out 10000 walkings every 5 °.

Figure 15 is process flow diagram of the present invention.

Embodiment

Below in conjunction with technical scheme and accompanying drawing, the present invention is further described.The size length of the inspection prober of the present embodiment is 1.5m, wide b=1.0m, and gradient θ is restricted to 20 °, and obstacle climbing ability (vertical direction) h is 20cm.

The selection of A, inspection prober device anchor point and travel direction

The first step, with one, 15 touch-down zone of moonscape Apollo 60*60m ²terrain data be example, selecting the space length of every pixel representative is 60mm, can set up the celestial body landform digital elevation figure DEM of the resolution of 1000*1000 shown in Fig. 1, the minimum height value Z in this region _minfor-1.7m, maximum elevation value Z _maxfor 1.45m, the gray level of 0-255 in corresponding celestial body landform digital elevation figure DEM, every gray level represents the floor level of 12.35mm.

Second step, the rotation interval of celestial body landform digital elevation figure DEM can arbitrarily be adjusted in mean free path computation process, and interval is less, and mean free path is calculated more accurate, and this example is finally chosen as 5 ° of intervals, has carried out 72 rotations.Fig. 2-9 are depicted as 5 °, 10 °, 20 °, 30 °, 45 °, 90 °, 180 °, the 315 ° celestial body landform digital elevation figure DEM rotation examples of picking out.

The 3rd step, fixed vertical is upwards travel direction, in every width celestial body landform digital elevation figure DEM, the random starting point of selecting is as the central point of inspection prober starting, extracts the lunar surface altitude figures in car body drop shadow spread around central point according to car body size length * wide=1.5m * 1.0m in celestial body landform digital elevation figure DEM.As shown in figure 10.

B, inspection prober car body view field passability are judged

The first step, utilizes least square method to carry out space plane matching to the lunar surface altitude figures in car body drop shadow spread, and as shown in figure 11, the space line equation obtaining is z=ax+by+c, then according to space plane parameter, obtains the grade information of this view field, the gradient the climbing capacity of inspection prober is 20 °, if the gradient θ calculating is greater than 20 °, shows that car body view field can not pass through.

Second step, in the region of overall width * 20/tan shown in Figure 12 (20 °), searches for minimum height value and maximum elevation value, if the difference of the two is greater than the 20cm that inspection prober obstacle climbing ability limits, judges that car body view field can not pass through.

If within the scope that the value of slope calculating and difference maximum, minimum height value all can realize at inspection prober, judge that car body view field can pass through.

C, mean free path are calculated

In simulation process, by take 5 ° be interval rotation 72 width celestial body landform digital elevation figure DEM carry out respectively 10000 walkings, the craspedodrome of take runs into can not be by locating as terminal, obtain the longest air line distance that at every turn can travel, the result of 72*10000 calculating is sued for peace, and then average, can obtain the mean free path of final inspection prober in this landform region.For example, proceed to the result of 3000 free path calculating in the celestial body landform digital elevation figure DEM Figure 13 shows that 315 ° of rotations, in figure, black line is the car body edge track that direction is passed by vertically upward.Figure 14 is the result of calculation curve of mean free path in all directions, add and average after can to obtain the mean free path of selected inspection prober in this landform region be 9.23m.

Claims (1)

1. inspection prober mean free path computing method that are directed to complex-terrain environment, is characterized in that: comprise the following steps:

The selection of A, inspection prober anchor point and travel direction

A1, generation celestial body landform digital elevation figure DigitalElevationMap, DEM

The terrain data of certain celestial body surf zone of being described by digital elevation model is one group of tri-vector finite sequence, is: V with the formal description of function _i=(X _i, Y _i, Z _i), wherein, X _i, Y _iplanimetric coordinates, Z _ix _i, Y _icorresponding elevation, i=1,2,3 ..., n; In Matlab software, first programme and realize the scope extraction of planimetric coordinates and elevation, find directions X minimum value X _minwith maximal value X _max, Y-direction minimum value Y _minwith maximal value Y _max, Z direction minimum value Z _minwith maximal value Z _max; Then, determine the bulk of each pixel representative in map and the height value of different gray-scale value representatives, set up the digital elevation figure describing with gray level image, wherein, the gray-scale value of 0-255 and Z _min-Z _maxbetween be linear mapping relations;

A2, selection travel direction

The mean value that mean free path is the free path repeatedly selecting at random reference position and travel direction and obtain, need to expend very long simulation time; In order to reduce algorithm complex, improve simulation velocity, select to press fixed angle interval rotation celestial body landform digital elevation figure DEM, the method for then all travelling along fixed-direction on every width figure averages free path and calculates, the complicacy that while avoiding random choice direction to travel, car body view field is calculated;

A3, random selecting point travel

After definite fixedly travel direction, in every width celestial body landform digital elevation figure DEM, the random starting point of selecting is as the central point of inspection prober starting, extracts the central point landform altitude data in car body drop shadow spread around according to car body size in celestial body landform digital elevation figure DEM;

B, inspection prober car body view field passability are judged

Passability judgement comprises two aspects, the one, and gradient restriction, another is vertical height restriction, both are all single free path and calculate the decision condition stopping; If inspection prober is wide, be b, vertical height is h, and the gradient that can ascend is restricted to θ; Wherein, step B1 is that the gradient is judged, step B2 is that vertical height is judged; When both are all inspection prober by result of determination, can pass through, judge that car body view field can pass through;

Landform altitude data in B1, selection car body drop shadow spread, utilize least square method to carry out space plane matching, the space plane parameter obtaining according to matching obtains the grade information of car body view field, according to the driveability of inspection prober, the gradient is greater than θ and is and can not passes through this region, calculates one of decision condition stopping as single free path;

B2, in the region of the anterior overall width b*h/tan θ of view field, search for minimum height value and maximum elevation value, if both differences are greater than h, think and exceed obstacle climbing ability scope, as single free path, calculate another decision condition stopping;

C, mean free path are calculated

During each simulation calculation free path, take keeps straight on runs into and can not repeatedly add up rear sum-average arithmetic by locating, as terminal, to obtain the longest air line distance that single can travel, and just can obtain mean free path.